The present invention relates to scalable mass storage and more particularly to a hierarchical arrangement of array controllers to provide a simplified upgrade path to facilitate high capacity storage capabilities via a single virtual device.
Enterprise resource planning systems and other sophisticated corporate data processing systems have gained substantial importance in recent years. Specifically, many corporate management theories posit that the success of an organization is directly related to the ability to gather and process enterprise information in an efficient and organized manner. To fulfill these goals, certain software companies have produced information management products such as RP/3 and the like. These types of software systems manage enormous amounts of information. Management of inventory levels, customer purchasing information, accounting data, employment information, and various other databases requires significant storage capacity. In addition, e-commerce has placed a premium upon transferring ordinary business operations to electronic work flows, thereby creating further storage capacity requirements. In addition, increased processing speed and capacity places greater demands upon storage resources.
Enterprises have attempted to provide large storage capacity for such enterprise applications in a number of ways. For example, the most rudimentary manner is to provide xe2x80x9cjust a bunch of disksxe2x80x9d (JBODs). In this situation, an enterprise purchases a number of discrete drive units that individually provide storage capacity. In addition, JBODs utilize operating system resources to make the assemblage of disk units appear as a single device. For example, a UNIX platform may interface with each disk unit. Also, the UNIX platform manages storage on the disk units. Files are written to a individual disk unit by sending the file to the UNIX platform. The UNIX platform then handles the controller functions. This approach is problematic in many respects. First, the maintenance and on-going performance optimization of the UNIX platform requires sophisticated technical personnel. Moreover, this approach is not operationally efficient as storage capacity reaches significant levels. Accordingly, JBODs are unable to operate beyond certain storage level limits.
Also, disk arrays have been designed to address storage requirements. An exemplary disk array system is described in commonly assigned U.S. Pat. No. 5,392,244, entitled xe2x80x9cMEMORY SYSTEMS WITH DATA STORAGE REDUNDANCY MANAGEMENT,xe2x80x9d the disclosure of which is incorporated herein by reference. In essence, a disk array is a system that utilizes a number of discrete disks and interfaces with a host system or systems in such a manner that the assemblage of discrete disks appears as a single disk system. Disk arrays present numerous advantages. For example, disk arrays are highly redundant. If a particular discrete disk fails, the remaining portion of the disk array remains in operation. Moreover, disk arrays permit data mirroring, i.e. the same data may be stored upon more than one disk to provide greater redundancy against discrete disk failure. Accordingly, the probability of data loss is thereby reduced. Also, the operation of the controller functions occurs automatically. Thus, it is not necessary to allocate significant technical personnel resources to maintain disk arrays.
Despite their obvious improvement over JBODs, known disk array systems possess certain limitations. Most importantly, disk arrays provide limited expansion capability. When storage capacity requirements become very large, smaller disk array systems may be replaced by a bunch of disks arrays connected via a hub. However, this defeats some of the inherent advantages of the disk array approach. Alternatively, larger disk arrays may be substituted when an organization""s storage needs exceed current capacity. However, this is an expensive approach in that it causes the smaller disk arrays to become obsolete.
The present invention is directed to a system and method which utilize a hierarchical arrangement of storage controllers to provide a scalable storage system. The scalable storage system is preferably capable of causing a very large amount of discrete disk units to appear as a single drive. The present invention organizes the hierarchical structure by preferably providing a series of disk arrays in parallel via Fiber Channel connections to form a xe2x80x9cvirtual disk.xe2x80x9d This organization of disk arrays is called a virtual disk, since it is configured through the use of a controller to appear to function as a single disk. The next level in the hierarchical structure is created by connecting a series of virtual disks and a higher level controller in parallel utilizing a plurality of Fibre Channel connections. Again, the higher level controller is preferably configured such that the assemblage of storage devices appears as a single, albeit enormous, disk. Also, the present invention preferably disposes increasingly sized RAM caches in the controllers to increase performance. Moreover, the present invention may utilize wave division multiplexing (WDM) to communicate to a file server via a higher level controller.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.